Ground fault interrupts for solid state power controllers

ABSTRACT

A solid state power control scheme is provided with a ground fault interrupt function. Essentially, if a neutral wire is associated with the power supply, the current is sensed in that neutral wire. The sensed neutral wire current is subtracted from a summed current on the power supply lines. If that result is greater than a predetermined limit, then the ground fault function is actuated and the circuit is opened. For power supplies, both those with and without neutral wires, the current is sensed by a shunt resistor on the power supply line.

BACKGROUND OF THE INVENTION

Solid state power controllers for controlling the flow of power tovarious components require a ground fault interrupt to open the powersupply if undesired conditions are sensed. The use of such ground faultinterrupts is becoming particularly important for solid state powercontrollers utilized with components in an aircraft.

It is known in a standard ground fault interrupt, that the current onthe power supply lines is summed and compared to a maximum. If thesummed currents on the several power supply lines exceed a predeterminedmaximum, then a ground fault interrupt opens to open a circuit andprevent the flow of further power.

Several distinct types of power supplies are commonly utilized. As anexample, there are three-phase power supplies both with and without afourth neutral wire. Further, there are single phase power supplies, ordual phase power supplies. Each of these different types of power supplymight be associated with a particular optimum method of sensing acurrent which should trigger a ground fault interrupt.

SUMMARY OF THE INVENTION

The present invention utilizes a remote sensor on a neutral wire, forany power supplies that incorporate a neutral wire. The current power onthe several power lines (e.g., three in a three-phase power supply) issummed. The current sensed by the remote current sensor on the neutralline is subtracted from that summed amount, and the result is comparedto a predetermined maximum. If the result is higher than the maximum,then the controller is activated to open the circuit, and interruptpower supply.

The power supply having the neutral line would include not justthree-phase power but also a single phase load, which is typicallyassociated with a neutral line. The present invention thus provides anaccurate and very reliable method of identifying a situation whereinpower supply should be interrupted.

In another feature of this invention, the sensor utilized to sense theline current is a shunt resistor included into the line. The prior arthas utilized sensors that are somewhat more complex and expensive,mostly common mode current transformers.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a schematic view of a power supply for several componentssuch as may be utilized on an aircraft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A complex power supply system 20 is illustrated schematically in theFIGURE. A three-phase generator 22 supplies power to a number ofcomponents 24, 25, 28 and 30. These components may be various componentssuch as are found on an aircraft. Examples may be motors, power valves,etc. The four identified components each receive a distinct type ofpower from the power supply 22. Individual solid state controllers 26,42 and 60 control the flow of the power to the individual components.Each of the controllers has ground fault interrupt capability, and thecontrollers disconnect the circuits should conditions indicate that aground fault condition may be occurring.

The solid state controller 26 incorporates three power supply lines 28,30 and 32. This controller is not provided with a neutral wire. Each ofthe lines 28, 30 and 32 are provided with a switch 34 (electromechanicalor solid state). A shunt resistor 36 and a sensor 38 are associated witheach of the power supply lines 28, 30 and 32. A ground fault line 40 isalso associated with one of the power supply lines indicating thepotential ground fault path.

In this invention, as power flows to the component 24, the sensors 36sense the current in each of the three lines 28, 30 and 32. Those threecurrents are summed by the solid state power controller, and the sum iscompared to a maximum. If the sum exceeds that maximum, then a decisionis made to open the circuit and utilize the ground fault interruptfeature. The present invention utilizes the shunt resistor as thesensor, and is a simplification over the prior art, mainly using currenttransformers.

The solid state power controller 42 is associated with a three-phasepower line having a neutral wire 50. Here, the power supply lines 44, 46and 48 are each associated with a shunt resistor sensor 36, along withan interrupt switch 34 as is the case with the controller 26. However,as can be appreciated, a neutral wire 50 is also associated with thethree-phase power lines. A remote current sensor 54 including a resistor52 senses the current in the neutral line 50. The remote current sensoris somewhat intelligent and able to communicate with controller 42. Aground fault 56 bypasses current of the power supply lines to theneutral, without going through the load. In this application, thecurrent sensed in the neutral line is subtracted from the summedcurrents in the three lines 44, 46 and 48. (The same equation applies tothe calculation in the above paragraph, but the neutral wire current iszero.) The resulting number is then compared to a maximum amount, andthe switches 34 are opened should the calculated current number exceedthe maximum. The present invention provides an accurate and responsiveway of identifying a situation at which a ground fault condition shouldcause an interruption on a three-phase power line having a neutral wire.

The controller 60 is associated with two components 28 and 30. A powersupply line 61 is a single phase load and would also be provided with aneutral wire at 62. A ground fault 68 would bypass current from thepower line to the neutral without going through the load. A remotecurrent sensor 64 is associated with the neutral line 62. Again, thecurrent sensed by the remote current sensor 64 is subtracted from thecurrent sensed in the line 61. If the remainder exceeds a predeterminedmaximum, a decision is made that a ground fault condition is occurring.

A two-phase load is also shown powering the component 30 without aneutral wire. The power supply line 70 and 72 have their currents summedas in the prior art and compared to the maximum. Switches 34 are openedshould that summed amount exceed the predetermined value.

In sum, the present invention provides a reliable and accurate method ofproviding a ground fault interrupt function in a complex power supply.On power supplies including a neutral wire, the neutral wire current isutilized along with the current sensing each of the power lines. Inanother feature, a shunt resistor is utilized to measure the current ineach of the power supply lines. Both of these features provide valuablebenefits, and may be utilized separate from each other.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill in this art would recognize that certainmodifications would come within the scope of this invention. For thatreason, the following claims should be studied to determine the truescope and content of this invention.

1. A solid state power controller having a ground fault interruptfunction comprising: a controller for receiving at least one powersupply line, and having at least one neutral wire, said controller beingoperable to receive a sensed current in said at least one power supplyline, and in said neutral line, and compare the two received currents toa predetermined limit, said controller being operable to interrupt powersupply to said at least one power supply line should the limit beexceeded.
 2. The controller as set forth in claim 1, wherein saidneutral line is provided with a current sensor at a location remote fromsaid controller.
 3. The controller as set forth in claim 1, wherein saidat least one power supply line includes at least two power supply lines.4. The controller as set forth in claim 3, wherein said at least twopower supply lines include three power supply lines at three differentphases.
 5. The controller as set forth in claim 1, wherein a resistor isassociated with said at least one power supply line, and said shuntresistor sensing the current flowing through said at least one powersupply line.
 6. A power controller comprising: at least one power supplyline for transmitting received power to an associated component, said atleast one power supply line being provided with a shunt resistor sensorfor sensing a current flowing through said at least one power supplyline, and the sensed current being compared to a limit, and saidcontroller opening a ground fault interrupt switch should said sensedcurrent exceed said limit.
 7. The controller as set forth in claim 6,wherein said at least one power supply line includes at least two powersupply lines.
 8. The controller as set forth in claim 7, wherein said atleast two power supply lines include three power supply lines at threedifferent phases.
 9. A plurality of components associated with anaircraft comprising: a plurality of components each being provided witha solid state power controller for supplying power to said plurality ofcomponents, at least one of said solid state power controllers includinga controller for receiving at least one power supply line, and at leastone neutral wire, said controller being operable to receive a sensedcurrent in said at least one power supply line, and in said neutralline, and compare the two received currents to a predetermined limit,said controller being operable to interrupt power supply to said atleast one power supply line should the limit be exceeded.
 10. Theplurality of components as set forth in claim 9, wherein said neutralline is provided with a current sensor at a location remote from saidcontroller.
 11. The plurality of components as set forth in claim 9,wherein said at least one power supply line includes at least two powersupply lines.
 12. The plurality of components as set forth in claim 11,wherein said at least two power supply lines include three power supplylines at three different phases.
 13. The plurality of components as setforth in claim 9, wherein a resistor is associated with said at leastone power supply line, and said resistor sensing the current flowingthrough said at least one power supply line.